The Maasai tribesman have also been warned to keep their private parts covered up and not to spit or grab Brits’ jewellery.
The four-page guide by Greenforce charity workers tells the group not to follow their hunting instincts if they see a cow, pig or sheep in a field.
It says: “It is important to remember these animals are owned by someone and are looked after.”
The men from a remote village in Tanzania will do the 26-mile run on April 13 in robes and carrying shields and spears. They are raising money for life-saving supplies back home.
But the guide tells them: “It is illegal to show certain parts of the body so it is important to wear underpants.” It says when nature calls they should find a toilet rather than a bush.
It also advises them not to spit in public — except in a sink or at a tree “if no one is looking”. It adds: “If you take and wear something someone else has, like a bracelet, they will find it unusual"!
The guide also warns that Brits “seem sillier” when they drink alcohol.